One of the products known in the conventional art is the image forming apparatus of electrophotographic process using a liquid developer. In such an image forming apparatus, an electrostatic latent image is formed on the photoreceptor and is developed using the liquid developer, whereby a toner image is formed. This toner image is transferred onto paper and is then fixed thereon.
The liquid developer is formed by dispersing toner of a high concentration made of resin and pigment in a carrier solution as an insulating solution such as silicone oil. When developing an electrostatic latent image using this liquid developer, a thin layer of developer in units of microns is formed on a developer carrier such as a development roller. This developer formed as a thin layer is brought in contact with a photoreceptor.
When a liquid developer is used for development as described above, it is important to form a uniform thin layer using a developer of a constant concentration in order to form images of constant concentration. To put it another way, the concentration of the liquid developer must be kept constant.
A method of calculating the developer concentration by detecting the light transmittance of the developer (Japanese Unexamined Patent Application Publication No. H09-281808, Japanese Unexamined Patent Application Publication No. H11-73029 and Japanese Unexamined Patent Application Publication No. H10-3221) is a technique known in the conventional art to measure the concentration of a developer for the purpose of maintaining the concentration of a liquid developer constant. However, a method of calculating the concentration of the developer by light transmittance has the disadvantage of poor accuracy in measuring the concentration of the highly concentrated developer. This is attributable to the fact that, when the concentration of the developer is low, the light transmittance exhibits a big change in response to changes in concentration, but when the concentration is high, the light transmittance is reduced and saturated.
The U.S. Pat. No. 6,131,001 discloses a technique of measuring the concentration of the highly concentrated developer using the viscosity thereof. The methods of measuring the viscosity of the developer adopted in the technique disclosed in this document include obtaining the viscosity from the difference in pressure of the developer in a pipe, installing a viscometer in the tank for storing the developer, and obtaining the viscosity from the torque resulting from the flowing developer. Further, the Japanese Unexamined Patent Application Publication No. 2006-154541 is provided with a concentration detecting rotary member in contact with the liquid developer. It discloses the art of obtaining the concentration of the developer by detecting the current or speed of the motor driving this rotary member. However, the method of using the developer viscosity has a disadvantage in that viscosity property value is changed if there is a change in the liquid developer temperature (hereinafter referred to as “liquid temperature” as well).
Thus, in the aforementioned Japanese Unexamined Patent Application Publication No. 2006-154541, a temperature sensor for detecting the liquid developer temperature is provided, and toner supply is controlled based on the 3D map representing the relationship between the motor current, toner concentration and temperature. However, the temperature characteristics are changed by a change in the type and lot of the liquid developer, and therefore, high-precision adjustment cannot be ensured by a fixed correction map.
The Japanese Unexamined Patent Application Publication No. 2004-322496 discloses the technique, wherein information on ink quality is indicated on the ink cartridge, and the image formation conditions are changed in response to the quality information. However, a great number of correction tables must be prepared to use this technique to correct the temperature characteristics of the liquid developer.
The Japanese Unexamined Patent Application Publication No. H07-174607 discloses an instrumental error correction apparatus of a flowmeter for kerosene and others. This instrumental error correction apparatus specifies the type of the fluid as an object to be tested. The instrumental error is corrected based on the viscosity correction data corresponding to the temperature for each type and the viscosity data corresponding to the current temperature. However, a great number of correction tables must be prepared to use this technique to adjust the concentration of the liquid developer.